Various technologies exist for custom fitting a hearing aid for a patient. Variations of hearing aids exist including behind the ear (“BTE”) with a custom ear mold attached towards the hearing aid, and custom products which includes, in the canal (ITC) as well completely in the canal (“CIC”). In order to custom fit these, or other types of hearing aids, an impression is made of the patient's external auditory meatus (“EAM”), the ear canal, or auditory canal extending from the patient's external ear opening in the pinna (the visible part of the ear that resides outside of the head) to the tympanic membrane (eardrum). An ear impression is a physical replica of a portion of the ear created by injecting impression material into the ear canal and external ear cavities, such as the concha and helix areas of the ear. Impression materials may include liquid-powder (ethyl methacrylate) and silicone-based materials.
There is a risk to the patient any time foreign material is introduced into the auditory canal. In particular, there is a risk of damaging the tympanic membrane located in the auditory canal should the tympanic membrane be contacted by the impression materials. In addition, impression materials may cause allergic reactions in some patients. Contacting, perforating, or otherwise damaging the tympanic membrane can cause considerable pain for the patient, and may increase chances of the patient developing a middle ear infection. In order to address the risk of impression materials contacting the tympanic membrane, an oto-block may be inserted into the ear in advance of the impression materials. An oto-block is typically a cotton ball or sponge attached to a thread that is placed into the auditory canal to prevent impression material from going further into the ear canal than required while conducting an ear mold impression. The oto-block size is important to ensure that the impression material does not pass the oto-block, but oto-blocks are not always completely effective at blocking impression materials.
Another problem is that in order to obtain a usable impression, the impression materials must solidify before they may be removed from the auditory canal. As the impression material solidifies, pressure in the patient's auditory canal increases. Although this may cause discomfort in patients of all ages, children may be particularly susceptible to pain or discomfort while the impression material solidifies. The patient must remain at least relatively stable while the oto-block is being inserted, while the impression material is being inserted, while the impression material solidifies, and while the impression material is being removed. Any patient, but particularly children, may resist any of these actions and may have to be restrained or assisted by a clinician, parent, guardian. Furthermore, once the oto-block is in place, it is important that the patient not move or remove the oto-block.
A further problem is that it is preferable to treat auditory disorders as early in a person's life as possible once diagnosed. However, certain conditions existing in a patient's auditory canal may delay the making of an impression. Infant, toddler, and preschool children are prone to ear infection during childhood development, particularly between the ages of 6 months and 3 years. Not only can impression material increase a child's risk of developing an ear infection, but an existing infection may need to be treated prior to an impression being taken. Other problems occurring in young or older children may include inflammation and fluid or cerumen (earwax) build-up in the middle ear or external ear. Any of these conditions may prevent an ear mold impression from being taken until the condition is treated, either because making an impression would be too painful while under the effects of the condition, or the condition may cause constriction or other deformation in the shape the auditory canal for the purposes of impression. Delaying the impression process may be problematic for children since doing so would delay the overall timeframe for treating the child's cognitive auditory issues or deficiencies. Especially in children, cognitive auditory treatment is most effective when performed early as plasticity development differs from children and adults. Where a child receives appropriate auditory amplification through treatment, it will have a large impact towards central auditory brain development, critical at least during the first two years of a child's life. If the child has hearing loss during this period, the child is likely to have a delayed ability to adapt when compared with children without cognitive auditory disorders. A child with hearing loss should therefore receive cognitive auditory treatment as soon as possible. With early treatment, the child's auditory brain development is able to revert back to normal or near normal central pathway development. With adults, once hearing loss progresses over a long period without treatment, the ability to alter near normal central auditory brain development will require a significantly greater amount of time. This process may be referred to as the acclimatization period, which has been shown to be faster in children than in adults. During this period, adults may require time adjusting towards extrinsic signals, or amplification, which has altered the central auditory pathways towards the brain. However, an adult with acquired hearing loss should already have prior knowledge and understanding of language, which would assist in allowing the adult to understand speech intelligibility without having all audible sounds towards speech.
A current preferred practice for making an ear impression may involve several items including: an otoscope with speculum; an ear light with removable tip; an oto-block with thread; a mixing bowl or wax pad; a spatula; blunt-end tweezers; blunt-end scissors; bite-blocks; a syringe or impression gun; and a variety of impression materials. Traditionally, the steps of inserting an oto-block, mixing impression materials, and removing the ear mold impression after solidification require at least 10 minutes for a single ear. In addition, depending on the density and shore of the ear mold impression, the traditional method requires clinicians to have good manual dexterity to insert impression material if an impression gun is not available. Coordination and release of impression material into the EAM all the way towards the pinna is also required to achieve an airtight seal. Pressure created from the impression material solidifying increases the risk of perforating the tympanic membrane. Recovery time from a perforated tympanic membrane may be long and painful.
In the current preferred practice, once the impression has solidified and is removed from the patient, the impression may be sent by mail to the hearing aid manufacturer for development of a corresponding prosthetic product using the replicated impression. Alternatively, a 3D image of the impression may be created and transmitted to the hearing aid manufacturer. The 3D image may be created by scanning the impression using an optical coherence tomography device (“OCT”). An OCT device is a non-invasive imaging system which may be used to collect high-resolution, three-dimensional tissue images from beams of light. This is a multi-step process by first taking the physical impression of the EAM and secondly, taking the EAM impression to the OCT to create a 3D imaging file from the impression.
Another problem with the current practice of creating an ear mold using impression materials is that errors may exist including incorrect technique used during measurement and improper use of the impression tools. Often, these errors will not be identified until after the hearing aid device is produced and an attempt to fit the device in the patient's ear is made.
An invisible-in-the-canal (“IIC”) device may be designed to be positioned millimeters away from the tympanic membrane in the EAM. If a patient is subjected to the traditional method of ear mold impression, the impression materials reach only millimeters away from the tympanic membrane, which can be very uncomfortable for the patient. Discomfort is not the only issue, as an ear impression that extends 10-12 mm beyond the second bend in the EAM is required for an accurate and comfortable fit of an IIC device. While no special equipment is necessarily required for IIC impressions, instrumentation to illuminate and view the ear canal beyond the second bend is valuable. Furthermore, silicone impressions may be taken with a high flow and a low viscosity material will typically fill the entire canal accurately and completely. A flattened oto-block may also be placed deep in the canal, very near the tympanic membrane.
Cepholometric radiography may also be used. A radiographic marker is placed in the patient's EAM and mounted on the ear post in the EAM. An ear canal blocker is also required.
A material socket may be used and a radiographic marker placed in the EAM.
Infrared light technology may be used in order to generate a 3D image of the EAM. Excellent positioning of the probe head is required in order to obtain a direct pathway in the EAM is required in order to replicate the EAM in a 3D format. The OCT method of reconstructing a 3D image of the EAM has limitations along with the infrared light technology. Infrared light technology works best only when conditions are met such as a direct line of site. At any time if the probes' infrared light position is misaligned, it will be unable to reconstruct the image of the ear as the pathway is not within line of sight. Also, the EAM varies from patient to patient where often times the EAM bends are not within line of site. OCT method of the reconstruction process requires good positioning of the probe head where the light source is emitted. Thus, this approach is not effective at passing second or third bends, if existing, in the EAM as a direct path is not obtainable. Additionally, the 3D images itself will require some manipulation in order extract the relevant shape of the EAM from the images. Cepholometric radiographic imaging is limited in this way as well. Also, if any cerumen or foreign object is within the pathway of the EAM, the OCT method of scanning would be unable to capture the EAM beyond this point.
Existing methods of replicating the pinna and or EAM requires some form of object implanted in the ear in order to achieve replicating for prosthetic development for the treatment of disorders or protection of the human auditory system. Accordingly, there is a need for a less invasive, less time consuming, yet accurate method of producing auditory canal implants that is not delayed by the presence of matter within the auditory canal.